WebUSB is a new web standard, and is currently supported by Google Chrome, Microsoft Edge, and Opera browsers. Chrome browser is preferred, and has been tested on Chrome OS, Windows, Mac OS, and Android platforms.
The following boards are recommended.
Users have also reported having success with a wide variety of boards. Chances are any MicroPython board with REPL over USB Serial should work. If you have a different board, please give it a try.